Hot Water Cylinder thermostat

Clodi

I have a solid-fuel Rayburn cooker which also provides hot water and central heating.
There is a Drayton HT53 thermostat on the HW cylinder which is supposed to turn the pump and zone valve on when the hot water reaches temperature.
It does not appear to be working as the pump and valve operate as soon as the power is on.
Looking at the thermostat's instructions there are 3 wires the common and 1 when the temp is reached which should turn on the pump and open the valve and the other which holds the valve closed and sends no power to the pump.
Putting a test light on the connections both 1 & 2 are live. Does this mean the thermostat is faulty? or is there any other way I should test it before replacing the unit.
Thanks

John.G

A normal cylinder stat cuts the power to the zone valve and the zone valve then springs closed, it may also then stop the pump but same pumps (and boilers) are stopped/started then from a separate set of contacts in the zone valve actuator.

So if stat is attached to the cylinder it switches the power ON on falling temperature and switches the power off on rising temperature, the common terminal C (permanent live) and 1 (switched live) do the switching.

If the stat is used to open the zone valve on RISING temperature like a solid fuel stove, then the stat is wired C (permanent live) and 2 (switched live) and would be attached to the flow pipe close to the stove.

Terminals 1 & 2 should never be live together, when 1 is live then 2 is not and vica versa.

Edit: its a EPH stat I was referring to which is marked C, 1 and 2. Others will be marked 1 (common) 2 (switched on falling temperature) and 3 (switched on rising temperature) so 2&3 in this case should never be live together.

Clodi

Thanks, I checked again and both 1&2 are pos at the sametime so I shall replace the thermostat.